This invention relates to a vinyl chloride type resin composition comprising a reinforcing agent, and a method of manufacturing same, and more particularly to such method and composition wherein impact strength and fabricability are substantially improved.
In the prior art, inorganic fillers have been used mixed together with various resins, such as PVC, to impart mechanical strength to the resin. For example, glass fibers and asbestos, have been used to impart various properties to polyvinyl chloride. However, use of such fillers, is not wholely satisfactory because of the unidirectionality of the tensile strength properties, namely, the tensile properties in the direction of flow are enhanced, but the tensile properties in the direction perpendicular to that of the flow is seriously degraded. Moreover, the impact resistance specially characteristic of the polyvinyl chloride resin is notably impaired by the use of such fillers.
A possible alternative is the use of mica or talc as a filler, since these materials have low anisotropy in properties. However, disadvantageously, mica is incapable of manifesting any reinforcing property and is low in impact strength, and hence is not practically useful. Talc has some reinforcing property but generally exhibits poor impact resistance. Use of very fine sized particles of talc can improve the impact resistance. However, such very fine sized particles are difficult to disperse uniformily in the resin during the steps of blending and molding. Thus, the composite mixture of, for example, PVC and the talc, suffers from dispersion of the properties. If the composite mixture is produced with very fine particles of talc to improve impact resistance, disadvantageously, the resistance has been found to be lowered to less than the impact resistance of pure unreinforced PVC. The different properties of the composite mixture, therefore stands in the way of practical use of such composite mixture of talc and PVC, wherein such composite mixture is by using conventional mixing and molding techniques.
The impact resistance of a composite mixture containing a blend of resin particles and dispersed inorganic particles can be improved by enhancing the uniformity of dispersion of the inorganic particles in the matrix, such as the PVC matrix. Since the particles of inorganic fillers are extremely small compared to the size of the matrix particles, being for example some hundreds of microns in the case of a suspension polymerized PVC, prior to the blending, it is difficult to mechanically uniformily disperse the the inorganic particles. If uniform dispersion is obtained by blending for a length of time sufficient to ensure thorough mixing, the amount of time expended would make such an operation practically and economically infeasible.
Also, the prior art has taught polymerization of resins in the presence of inorganic substances. For example, Japanese Patent Publication No. 11,661/1972 discloses a method of giving to a filler having a specific surface area of not less than 1 m.sup.2 /g a surface treatment using a vinyl polymer by adding to a suspension of said filler in water 0.5 to 40% based on the filler, of vinyl monomer and polymerizing the resulting mixed system. Although this method improves the mixed condition of the polymer and the filler, disadvantageously, the filler particles are expelled out of the polymer particles as the polymerization proceeds and upon completion of the polymerization, absolutely no filler particles were found to be embedded within the polymer particles. Japanese Patent Publication No. 2,659/1975 discloses a procedure which precludes otherwise possible decline of polymerization velocity by asbestos by adding to asbestos treated with silane 5% by weight of alcoholic water and a monomer and subjecting the resultant mixed system to bulk polymerization. Japanese Patent Publication No. 33,915/1975 discloses a study aimed at attaining dispersion of a stabilizer and a slidant as well as a filler in a system under polymerization. These prior methods are deficient in that the inorganic substances are not embedded or dispersed within the the polymer particles, nor is at least one surface of the inorganic substances in direct contact with the polymer particles without any intervening material therebetween. In some cases, the inorganic filler may partially adhere to the surface of the polymer particles, but with an intervening material between the filler surface and the polymer particle.
Inorganic substances by nature have poor affinity for organic substances. Thus, even when the inorganic substances are dispersed in a monomer blend or a monomer mixture blend, preparatory to polymerization, they are expelled from the organic particles with the progress of the polymerization. This is also true for talc, which is used in our invention. When polymerization is carried out by conventional methods, the talc will not become embedded within the polymer particles. They may, however, partially adhere to the surface of such polymer particles, but always with an intervening material between the talc surface and the surface of the polymer particle, for example. The produced composite having such partially adhered talc, for example, will have properties, e.g. impact resistance, which are no better than those of products obtained by mechanically mixing talc and polymer particles.
Thus, in summary, in the art there are disclosed compositions formed of a mechanical mixture of talc and polymer particles with intervening material therebetween, and compositions formed by conventional polymerization processes wherein talc may be partially adhered to the polymer particles, but with intervening material therebetween. It was not known in the prior art, any method which produced a composition of talc and vinyl chloride resin wherein the talc was in direct contact with the polymer particles without any intervening material between the talc and the polymer particle, nor was there known any method wherein the talc was caused to be embedded within the polymer particles. The prior compositions thus were deficient in inpact resistance and tensile strength.